1. Field of the Invention
The present invention relates to an ignition system which also controls the spark timing of a spark-ignition type internal combustion engine according to temperatures to thereby distribute a high-voltage surge to the spark plug at the correct instant.
2. Description of the Prior Art
In the past, two types of ignition devices have been incorporated in the conventional ignition systems: these are a centrifugal spark advance mechanism for controlling the ignition timing of the engine according to the engine speed and a vacuum spark advance mechanism which advances or retards the timing of the spark according to the engine intake manifold vacuum. These mechanisms have primarily had their origin in the conception that the correct ignition timing of an engine could be satisfactorily determined according to two controlling factors, that is, the engine speed and the engine intake manifold vacuum.
In actual operation of an engine, however, a driver frequently experiences such trouble that while there was no difficulty with the hot engine (with the engine temperature in terms of the cooling water temperature higher than about 40.degree. C.), there was an inconvenience with the cold engine in that not only the engine ran unsatisfactorily, but also the engine lacked acceleration or other transient performance and this was particularly true in the winter months.
Of course, it has been known in the art that the engine torque efficiency could vary with different engine temperatures. In order to look into the cause of such variations, the inventors have conducted various experiments and much research and discovered that even with the same load and the same number of revolutions the range of the spark timing which would ensure stable operation of the engine differed depending on whether the engine was cold or hot and that the lower the engine temperature the greater the spark advance would be required.